Chemical mechanical polishing slurry useful for copper/tantalum substrates

ABSTRACT

The present invention is a first CMP slurry including an abrasive, an oxidizing agent, a complexing agent, a film forming agent and an organic amino compound, a second polishing slurry including an abrasive, an oxidizing agent, and acetic acid wherein the weight ratio of the oxidizing agent to acetic acid is at least 10 and a method for using the first and second polishing slurries sequentially to polish a substrate containing copper and containing tantalum or tantalum nitride or both tantalum and tantalum nitride.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns chemical mechanical polishing slurries that areuseful when used in sequence for polishing a substrate including acopper portion and a tantalum portion. The invention includes a firstchemical mechanical polishing slurry including an abrasive, an oxidizingagent, a complexing agent and at least one organic amino compound. Theinvention also includes a second chemical mechanical polishing slurryincluding an abrasive, an oxidizing agent and a complexing agent wherethe weight ratio of oxidizing agent to complexing agent is greater than15. This invention also includes a method for using the first and secondchemical mechanical polishing slurries to sequentially polish asubstrate including a copper portion and a tantalum portion.

2. Description of the Art

Integrated circuits are made up of millions of active devices formed inor on a silicon substrate. The active devices, which are initiallyisolated from one another, are interconnected to form functionalcircuits and components. The devices are interconnected through the useof multilevel interconnections. Interconnection structures normally havea first layer of metallization, an interconnection layer, a second levelof metallization, and sometimes a third and subsequent level ofmetallization. Interlevel dielectrics such as doped and undoped silicondioxide (SiO₂), or low-k dielectrics tantalum nitride are used toelectrically isolate the different levels of metallization in a siliconsubstrate or well. The electrical connections between differentinterconnection levels are made through the use of metallized vias. U.S.Pat. No. 5,741,626, which is incorporated herein by reference, describesa method for preparing dielectric tantalum nitride layers.

In a similar manner, metal contacts are used to form electricalconnections between interconnection levels and devices formed in a well.The metal vias and contacts may be filled with various metals and alloysincluding titanium (Ti), titanium nitride (TiN), tantalum (Ta), aluminumcopper (Al—Cu), aluminum silicon (Al—Si), copper (Cu), tungsten (W), andcombinations thereof. The metal vias and contacts generally employ anadhesion layer such as titanium nitride (TiN), titanium (Ti), Tantalum(Ta), Tantalum nitride (TaN) or combinations thereof to adhere the metallayer to the SiO₂ substrate. At the contact level, the adhesion layeracts as a diffusion barrier to prevent the filled metal and SiO₂ fromreacting.

In one semiconductor manufacturing process, metallized vias or contactsare formed by a blanket metal deposition followed by a chemicalmechanical polish (CMP) step. In a typical process, via holes are etchedthrough an interlevel dielectric (ILD) to interconnection lines or to asemiconductor substrate. Next, a thin adhesion layer such as tantalumnitride and/or tantalum is generally formed over the ILD and is directedinto the etched via hole. Then, a metal film is blanket deposited overthe adhesion layer and into the via hole. Deposition is continued untilthe via hole is filled with the blanket deposited metal. Finally, theexcess metal is removed by chemical mechanical polishing, (CMP) to formmetal vias. Processes for manufacturing and/or CMP of vias are disclosedin U.S. Pat. Nos. 4,671,851, 4,910,155 and 4,944,836.

In a typical chemical mechanical polishing process, the substrate isplaced in direct contact with a rotating polishing pad. A carrierapplies pressure against the backside of the substrate. During thepolishing process, the pad and table are rotated while a downward forceis maintained against the substrate back. An abrasive and chemicallyreactive solution, commonly referred to as a “slurry” is applied to thepad during polishing. The slurry initiates the polishing process bychemically reacting with the film being polished. The polishing processis facilitated by the rotational movement of the pad relative to thesubstrate as slurry is provided to the wafer/pad interface. Polishing iscontinued in this manner until the desired film on the insulator isremoved. The slurry composition is an important factor in the CMP step.Depending on the choice of the oxidizing agent, the abrasive, and otheruseful additives, the polishing slurry can be tailored to provideeffective polishing to metal layers at desired polishing rates whileminimizing surface imperfections, defects and corrosion and erosion.Furthermore, the polishing slurry may be used to provide controlledpolishing selectivities to other thin-film materials used in currentintegrated circuit technology such as titanium, titanium nitride,tantalum, tantalum nitride, and the like.

Typically CMP polishing slurries contain an abrasive material, such assilica or alumina, suspended in an oxidizing, aqueous medium. Forexample, U.S. Pat. No. 5,244,534 to Yu et al. reports a slurrycontaining alumina, hydrogen peroxide, and either potassium or ammoniumhydroxide that is useful to remove tungsten at predictable rates withlittle removal of the underlying insulating layer. U.S. Pat. No.5,209,816 to Yu et al. discloses a slurry comprising perchloric acid,hydrogen peroxide and a solid abrasive material in an aqueous mediumthat is useful for polishing aluminum. U.S. Pat. No. 5,340,370 to Cadienand Feller discloses a tungsten polishing slurry comprisingapproximately 0.1 M potassium ferricyanide, approximately 5 weightpercent silica and potassium acetate. Acetic acid is added to buffer thepH at approximately 3.5.

U.S. Pat. No. 4,789,648 to Beyer et al. discloses a slurry formulationusing alumina abrasives in conjunction with sulfuric, nitric, and aceticacids and deionized water. U.S. Pat. Nos. 5,391,258 and 5,476,606disclose slurries for polishing a composite of metal and silica whichincludes an aqueous medium, abrasive particles and an anion whichcontrols the rate of silica removal. Other polishing slurries for use inCMP applications are described in U.S. Pat. No. 5,527,423 to Neville etal., U.S. Pat. No. 5,354,490 to Yu et al., U.S. Pat. No. 5,340,370 toCadien et al., U.S. Pat. No. 5,209,816 to Yu et al., U.S. Pat. No.5,157,876 to Medellin, U.S. Pat. No. 5,137,544 to Medellin, and U.S.Pat. No. 4,956,313 to Cote et al.

There are various mechanisms disclosed in the prior art by which metalsurfaces can be polished with slurries. The metal surface may bepolished using a slurry in which a surface film is not formed in whichcase the process proceeds by mechanical removal of metal particles andtheir dissolution in the slurry. In such a mechanism, the chemicaldissolution rate should be slow in order to avoid wet etching. A morepreferred mechanism is, however, one where a thin abradable layer iscontinuously formed by reaction between the metal surface and one ormore components in the slurry such as a complexing agent and/or a filmforming layer. The thin abradable layer is then removed in a controlledmanner by mechanical action. Once the mechanical polishing process hasstopped a thin passive film remains on the surface and controls the wetetching process. Controlling the chemical mechanical polishing processis much easier when a CMP slurry polishes using this mechanism.

Current copper containing substrates that are polished using chemicalmechanical polishing also use Ta and TaN adhesion layers. Ta and TaN arechemically very passive and mechanically very hard and thus difficult toremove by polishing. The use of a single slurry, which performs with ahigh Cu:Ta selectivity demand prolonged polishing times for Ta, i.e. asignificant overpolishing times for copper, during which there is asignificant degradation of dishing and erosion performance.

Several relevant Cu chemistries have been discussed in the openliterature, each failing to deliver a process which successfullyaddresses all of the key requirements of a chemical-mechanical polishingslurry useful for a substrate including both copper and tantalum. As aresult, there is a need for one or more CMP slurries that can be usedsuccessfully to polish copper and tantalum containing substrates.

SUMMARY OF THE INVENTION

The present invention is directed to a first chemical mechanicalpolishing slurry that is able to selectively polish the copper portionof a copper and tantalum or tantalum nitride containing substrate.

The present invention is also directed to a second chemical mechanicalpolishing slurry that is able to selectively polishing the tantalumand/or tantalum nitride portion of a copper and tantalum and/or tantalumnitride containing substrate.

Furthermore, this invention is directed to methods for sequentiallyusing a first and second chemical mechanical polishing slurry to polisha substrate including a copper portion and a tantalum and/or tantalumnitride portion.

Another aspect of this invention are first and second chemicalmechanical polishing slurry precursors that lack an oxidizing agent andthat are separately combined with an oxidizing agent prior to use togive a useful CMP slurries.

This invention is a first chemical mechanical polishing slurry. Thefirst chemical mechanical polishing slurry comprising at least oneabrasive, at least one oxidizing agent, at least one complexing agent,and at least one organic amino compound. A preferred embodiment of thefirst polishing slurry is a composition comprising alumina, at least oneoxidizing agent, tartaric acid, benzotriazole, and at least one organicamino compound.

This invention also includes a second chemical mechanical polishingslurry comprising at least one abrasive, at least one oxidizing agent,and acetic acid wherein the weight ratio of oxidizing agent to aceticacid is greater than about 10. A preferred embodiment of the secondchemical mechanical polishing slurry is a composition comprising anaqueous dispersion of alumina, hydrogen peroxide, from about 0.01 toabout 3.0 wt% acetic acid, and from about 0.01 to about 0.2 wt%benzotriazole wherein the weight ratio of oxidizing agent to acetic acidis greater than about 10, and wherein the slurry has a pH of from about4 to about 9.

This invention is also a method for polishing a substrate including acopper portion and a portion selected from tantalum or tantalum nitride.The method includes applying a first aqueous chemical mechanicalpolishing slurry comprising at least one abrasive, at least oneoxidizing agent, at least one complexing agent, and at least one organicamino compound to the substrate. A portion of the copper is removed fromthe substrate by bringing a pad into contact with the substrate andmoving the pad in relation to the substrate to give a partially polishedsubstrate. A second slurry is applied to the partially polishedsubstrate. The second chemical mechanical polishing slurry comprises atleast one abrasive, at least one oxidizing agent, and acetic acidwherein the weight ratio of oxidizing agent to acetic acid is greaterthan about 10. At least a portion of the tantalum or tantalum nitride isremoved from the partially polished substrate by bringing a pad intocontact with the substrate and thereafter moving the pad in relation tothe substrate to give a polished substrate.

DESCRIPTION OF THE CURRENT EMBODIMENT

The present invention relates to two chemical mechanical polishingslurries and to a method for using both slurries to sequentially polisha substrate including a copper portion and a tantalum or tantalumnitride portion at acceptable rates and with very few defects. Besidesbeing used in combination to polish a copper and tantalum containingsubstrate, the first chemical mechanical polishing slurry may be used topolish a copper or copper alloy containing substrate, and the secondpolishing slurry can be used to polish a tantalum or tantalum nitridecontaining substrate.

Before describing the details of the various preferred embodiments ofthis invention, some of the terms that are used herein will be defined.The chemical mechanical polishing slurry, (“CMP slurry”), is a usefulproduct of this invention that comprises an oxidizer, an abrasive, acomplexing agent, an organic amino compound, and other optionalingredients. The CMP slurry is useful for polishing a multiple levelmetallization which may include but are not limited to semi-conductorthin-films, integrated circuit thin-films, and for any other films andsurfaces where CMP processes are useful.

The terms “copper” and “copper containing alloys” are usedinterchangeably herein as it is within the understanding of one of skillin the art that the terms include but are not limited to substratescomprising layers of pure copper, copper aluminum alloys, and Ti/TiN/Cu,and Ta/TaN/Cu multi-layer substrates.

The terms “tantalum” and “tantalum containing alloys” are usedinterchangeably herein to refer to the tantalum and/or tantalum nitrideadhesion layer under the conductive layer such as a conductive copperlayer.

The first chemical mechanical polishing slurry is useful for polishingmetals, especially copper and copper alloy containing metal layersassociated with a substrate selected from the group including integratedcircuits, thin films, multiple level semiconductors, and wafers.

I. The First Chemical Mechanical Polishing Slurry

The first CMP slurry is most useful for polishing the copper portion ofa copper containing substrate of high rates. The first chemicalmechanical polishing slurry may be useful for polishing other metallayers besides copper.

The first CMP slurry includes at least one oxidizing agent. Theoxidizing agent aids in oxidizing the substrate metal layer or layers totheir corresponding oxide, hydroxide, or ions. For example, in the firstCMP slurry, the oxidizer may be used to oxidize a metal layer to itscorresponding oxide or hydroxide, e.g., titanium to titanium oxide,tungsten to tungsten oxide, copper to copper oxide, and aluminum toaluminum oxide. The oxidizing agent is useful when incorporated into thefirst CMP slurry to polish metals and metal based components includingtitanium, titanium nitride, tantalum, copper, tungsten, aluminum, andaluminum alloys such as aluminum/copper alloys, and various mixtures andcombinations thereof by mechanically polishing the metals to remove therespective oxide layer.

The oxidizing agents used in the first CMP slurry of this invention areone or more inorganic or organic per-compounds. A per-compound asdefined by Hawley's Condensed Chemical Dictionary is a compoundcontaining at least one peroxy group (—O—O—) or a compound containing anelement in its highest oxidation state. Examples of compounds containingat least one peroxy group include but are not limited to hydrogenperoxide and its adducts such as urea hydrogen peroxide andpercarbonates, organic peroxides such as benzyl peroxide, peraceticacid, and di-t-butyl peroxide, monopersulfates (SO₅ ⁼), dipersulfates(S₂O₈ ⁼), and sodium peroxide.

Examples of compounds containing an element in its highest oxidationstate include but are not limited to periodic acid, periodate salts,perbromic acid, perbromate salts, perchloric acid, perchloric salts,perboric acid, and perborate salts and permanganates. Examples ofnon-per compounds that meet the electrochemical potential requirementsinclude but are not limited to bromates, chlorates, chromates, iodates,iodic acid, and cerium (IV) compounds such as ammonium cerium nitrate.

Preferred oxidizing agents are peracetic acid, urea-hydrogen peroxide,hydrogen peroxide, monopersulfuric acid, dipersulfuric acid, saltsthereof, and mixtures thereof including mixtures of urea and hydrogenperoxide. A most preferred oxidizing agent is the combination ofhydrogen peroxide and urea.

The oxidizing agent may be present in the first chemical mechanicalpolishing slurry in an amount ranging from about 0.3 to about 30.0weight percent. It is preferred that the oxidizing agent is present inthe first CMP slurry of this invention in an amount ranging from about0.3 to about 17.0 weight percent and most preferably from about 0.5 toabout 12.0 weight percent.

An optional oxidizing agent is urea hydrogen peroxide. Because ureahydrogen peroxide is 34.5 wt % hydrogen peroxide and 65.5 wt % urea, agreater amount by weight of urea hydrogen peroxide must be included inthe first CMP slurry to achieve the desired oxidizer loading set forthabove. For example, a range of 0.5 to 12.0 weight percent oxidizingagent corresponds to a urea hydrogen peroxide weight three times asgreat or from 1.5 to 36.0 weight percent.

A first CMP slurry comprising urea hydrogen peroxide can be formulatedby a number of methods including combining urea peroxide with water, andby combining urea and hydrogen peroxide in an aqueous solution in a moleratio range of from about 0.75:1 to about 2:1 to give a urea hydrogenperoxide oxidizer.

The first CMP slurry of this invention forms a passivation layer on thesubstrate surface. Once a passivation layer is formed, it becomesimportant to be able to disturb the passivation layer in order to moreeasily abrade metal oxides from the substrate surface with the abrasivecomponent of the first CMP slurry. One class of compounds that isincluded in the first CMP slurry for disturbing the passivation layerare complexing agents. Useful complexing agents include but are notlimited to acids such as citric, lactic, malonic, tartaric, succinic,acetic, oxalic, and other acids, as well as amino acid and aminosulfuric acids, phosphoric acids, phosphonic acids, and their salts. Apreferred first CMP slurry complexing agent is tartaric acid.

The complexing agent will be present in the first CMP slurry in anamount ranging from about 0.2 to about 5.0 weight present and preferablyin an amount ranging from about 0.5 to about 3.0 weight percent.

The first CMP slurry of this invention will include at least one organicamino compound. The organic amino compounds absorb on the polishedsubstrate and inhibit the substrate material removal rate. Organic aminocompounds useful in the first CMP slurry include alkylamines, alcoholamines, amino acids, urea, derivatives of urea, and mixtures thereof.Preferred organic amino compounds are long chain alkylamines andalcoholamines. The term “long chain alkylamines” refers to alkylamineshaving from 7 to 12 or more carbon atoms including, for example,nonylamine and dodecylamine. Examples of useful alcoholamines include,but are not limited to monoethanolamine, and triethanolamine. Examplesof useful derivatives of urea include, but are not limited to biurea. Apreferred organic amino compound is the long chain alklyamine,dodecylamine. A preferred alcoholamine is triethanolamine.

The organic amino compound should be present in the first CMP slurry inan amount ranging from about 0.005 to about 10.0 weight percent. Morepreferably, the organic amino compound is present in the first CMPslurry in an amount ranging from about 0.01 to about 5.0 weight percent.

The first CMP slurry of this invention may include an optional filmforming agent. The film forming agent may be any compound or mixtures ofcompounds that are capable of facilitating the formation of apassivation layer of metal oxides and dissolution inhibiting layers onthe surface of the metal layer. Passivation of the substrate surfacelayer is important to prevent wet etching of the substrate surface.Useful film forming agents are nitrogen containing cyclic compounds suchas imidazole, benzotriazole, benzimidazole and benzothiazole and theirderivatives with hydroxy, amino, imino, carboxy, mercapto, nitro andalkyl substituted groups, as well as urea, thiourea and others. Apreferred film forming agent is benzotriazole (“BTA”).

The optional film forming agent may be present in the first CMP slurryof this invention in an amount ranging from about 0.01 weight percent toabout 1.0 weight percent. It is preferred that film forming agent ispresent in the first CMP slurry in an amount ranging from about 0.01 toabout 0.2 weight percent.

BTA, or other film forming agents included in the first CMP slurry maydestabilize the uniform dispersion of abrasive in the slurry. In orderto stabilize the first CMP slurry against settling, flocculation, anddecomposition, a variety of optional CMP slurry additives, such assurfactants, stabilizers, or dispersing agents, can be used. If asurfactant is added to the first CMP slurry, then it may be an anionic,cationic, nonionic, or amphoteric surfactant or a combination of two ormore surfactants can be employed. Furthermore, it has been found thatthe addition of a surfactant may be useful to reduce thewithin-wafer-non-uniformity (WIWNU) of the wafers, thereby improving thesurface of the wafer and reducing wafer defects.

In general, the amount of additive such as a surfactant that may be usedin the first CMP slurry should be sufficient to achieve effectivestabilization of the slurry and will typically vary depending on theparticular surfactant selected and the nature of the surface of themetal oxide abrasive. For example, if not enough of a selectedsurfactant is used, it will have little or no effect on first CMP slurrystabilization. On the other hand, too much surfactant in the CMP slurrymay result in undesirable foaming and/or flocculation in the slurry. Asa result, stabilizers such as surfactants should generally be present inthe slurry of this invention in an amount ranging from about 0.001% toabout 0.2% by weight, and preferably from about 0.001 to about 0.1weight percent. Furthermore, the additive may be added directly to theslurry or treated onto the surface of the metal oxide abrasive utilizingknown techniques. In either case, the amount of additive is adjusted toachieve the desired concentration in the first polishing slurry.Preferred surfactants useful in the first CMP slurry include dodecylsulfate sodium salt, sodium lauryl sulfate, dodecyl sulfate ammoniumsalt, and mixtures thereof. Examples of preferred surfactants includeTRITON® DF-16 manufactured by Union Carbide, and SURFYNOL® manufacturedby Air Products and Chemicals.

It is desirable to maintain the pH of the first CMP slurry of thisinvention within a range of from about 2.0 to about 12.0, and preferablybetween from about 4.0 to about 8.0 in order to facilitate control ofthe CMP process. The pH of the CMP slurry of this invention may beadjusted using any known acid, base, or amine. However, the use of anacid or base that contains no metal ions, such as ammonium hydroxide andamines, or nitric, phosphoric, sulfuric, or organic acids are preferredto avoid introducing undesirable metal components into the first CMPslurry.

II. The Second Chemical Mechanical Polishing Slurry

The second CMP slurry is formulated so that it exhibits a low polishingrate towards copper and a typical polishing rate towards tantalum ortantalum nitride. It is preferred, therefore, that the second CMP slurryhas a copper to tantalum polishing selectivity of less than about 2 to 1and most preferably and less than about 1 to 5.

The second CMP slurry includes at least one oxidizing agent. Theoxidizing agent aids in oxidizing the substrate metal layer or layers totheir corresponding oxide, hydroxide, or ions. For example, in thesecond CMP slurry, the oxidizer may be used to oxidize a metal layer toits corresponding oxide or hydroxide, e.g., tantalum to tantalum oxide.The oxidizing agent is useful when incorporated into the second CMPslurry to polish metals and metal based components including titanium,titanium nitride, tantalum, copper, tungsten, aluminum, and aluminumalloys such as aluminum/copper alloys, and various mixtures andcombinations thereof by mechanically polishing the metals with removalof the respective oxide layer.

The oxidizing agents used in the second CMP slurry of this invention areone or more inorganic or organic per-compounds. A per-compound asdefined by Hawley's Condensed Chemical Dictionary is a compoundcontaining at least one peroxy group (—O—O—) or a compound containing anelement in its highest oxidation state. Examples of compounds containingat least one peroxy group include but are not limited to hydrogenperoxide and its adducts such as urea hydrogen peroxide andpercarbonates, organic peroxides such as benzyl peroxide, peraceticacid, and di-t-butyl peroxide, monopersulfates (SO₅ ⁼), dipersulfates(S₂O₈ ⁼), and sodium peroxide.

Examples of compounds containing an element in its highest oxidationstate include but are not limited to periodic acid, periodate salts,perbromic acid, perbromate salts, perchloric acid, perchloric salts,perboric acid, and perborate salts and permanganates. Examples ofnon-per compounds that meet the electrochemical potential requirementsinclude but are not limited to bromates, chlorates, chromates, iodates,iodic acid, and cerium (IV) compounds such as ammonium cerium nitrate.

Non-exclusive examples of useful oxidizing agents include, but are notlimited to peracetic acid, urea-hydrogen peroxide, hydrogen peroxide,monopersulfuric acid, dipersulfuric acid, salts thereof, and mixturesthereof including mixtures of urea and hydrogen peroxide. A preferredoxidizing agent is hydrogen peroxide.

The oxidizing agent may be present in the second chemical mechanicalpolishing slurry in an amount ranging from about 0.3 to about 30.0weight percent. It is preferred that the oxidizer is present in thesecond CMP slurry of this invention in an amount ranging from about 0.3to about 17.0 weight percent and most preferably from about 1.0 to about12.0 weight percent.

One class of compounds that is included in the second CMP slurry arecomplexing agents. Useful complexing agents include but are not limitedto acids such as citric, lactic, tartaric, succinic, acetic, oxalic andother acids, as well as amino acid and amino sulfuric acids, phosphonicacids, phosphoric acids, and their salts. A preferred complexing agentis acetic acid. The complexing agent will be present in the CMP slurryof this invention in an amount ranging from about 0.1 to about 5.0weight present and preferably in an amount ranging from about 0.1 toabout 3.0 weight percent.

It is important that the second CMP slurry include a far smaller weightamount of complexing agent in comparison of the weight amount ofoxidizing agent in the slurry. The second CMP slurry should have aoxidizing agent to complexing agent weight ratio greater than about 10,and preferably greater than about 25.

The second CMP slurry of this invention may include an optional filmforming agent. The film forming agent may be any compound or mixtures ofcompounds that are capable of facilitating the formation of apassivation layer of metal oxides and dissolution inhibiting layers onthe surface of the metal layer. Passivation of the substrate surfacelayer is important to prevent wet etching of the substrate surface.Useful film forming agents are nitrogen containing cyclic compounds suchas imidazole, benzotriazole, benzimidazole and benzothiazole and theirderivatives with hydroxy, amino, imino, carboxy, mercapto, nitro andalkyl substituted groups, as well as urea, thiourea and others. Apreferred film forming agent is benzotriazole (“BTA”). The film formingagent may be present in the second CMP slurry in an amount ranging fromabout 0.01 weight percent to about 1.0 weight percent. It is preferredthat film forming agent is present in the second CMP slurry in an amountranging from about 0.01 to about 0.5 weight percent.

BTA, or other film forming agents included in the second CMP slurry maydestabilize the uniform dispersion of abrasive in the slurry. In orderto stabilize the second CMP slurry against settling, flocculation, anddecomposition, a variety of optional CMP slurry additives, such assurfactants, stabilizers, or dispersing agents, can be used. If asurfactant is added to the second CMP slurry, then it may be an anionic,cationic, nonionic, or amphoteric surfactant or a combination of two ormore surfactants can be employed. Furthermore, it has been found thatthe addition of a surfactant may be useful to reduce thewithin-wafer-non-uniformity (WIWNU) of the wafers, thereby improving thesurface of the wafer and reducing wafer defects.

In general, the amount of additive such as a surfactant that may be usedin the second CMP slurry should be sufficient to achieve effectivestabilization of the slurry and will typically vary depending on theparticular surfactant selected and the nature of the surface of themetal oxide abrasive. For example, if not enough of a selectedsurfactant is used, it will have little or no effect on CMP slurrystabilization. On the other hand, too much surfactant in the second CMPslurry may result in undesirable foaming and/or flocculation in theslurry. As a result, stabilizers such as surfactants should generally bepresent in the second slurry in an amount ranging from about 0.001% toabout 0.2% by weight, and preferably from about 0.001 to about 0.1weight percent. Furthermore, the additive may be added directly to theslurry or treated onto the surface of the metal oxide abrasive utilizingknown techniques. In either case, the amount of additive is adjusted toachieve the desired concentration in the first polishing slurry.Preferred surfactants include dodecyl sulfate sodium salt, sodium laurylsulfate, dodecyl sulfate ammonium salt, and mixtures thereof. Examplesof useful surfactants include TRITON® DF-16 manufactured by UnionCarbide, and SURFYNOL® manufactured by Air Products and Chemicals.

It is desirable to maintain the pH of the second CMP slurry of thisinvention within a range of from about 2.0 to about 12.0, and preferablybetween from about 4.0 to about 9.0 in order to facilitate control ofthe CMP process. The pH of the CMP slurry of this invention may beadjusted using any known acid, base, or amine. However, the use of anacid or base that contains no metal ions, such as ammonium hydroxide andamines, or nitric, phosphoric, sulfuric, or organic acids are preferredto avoid introducing undesirable metal components into the CMP slurry ofthis invention. It is most preferred that the second CMP slurry has a pHof from about 4 to about 7.5.

III. The Abrasive

The first and second CMP slurries of this each invention include anabrasive. The abrasive is typically a metal oxide. The metal oxideabrasive may be selected from the group including alumina, titania,zirconia, germania, silica, ceria and mixtures thereof. The first andsecond CMP slurries of this invention preferably each include from about0.5 to about 15.0 weight percent or more of an abrasive. It is morepreferred, however, that the first and second CMP slurries of thisinvention include from about 1.5 to about 6.0 weight percent abrasive.

The metal oxide abrasive may be produced by any techniques known tothose skilled in the art. Metal oxide abrasives can be produced usingany high temperature process such as sol-gel, hydrothermal or, plasmaprocess, or by processes for manufacturing fumed or precipitated metaloxides. Preferably, the metal oxide is a fumed or precipitated abrasiveand, more preferably it is a fuimed abrasive such as fumed silica orfumed alumina. For example, the production of fuimed metal oxides is awell-known process which involves the hydrolysis of suitable feedstockvapor (such as aluminum chloride for an alumina abrasive) in a flame ofhydrogen and oxygen. Molten particles of roughly spherical shapes areformed in the combustion process, the diameters of which are variedthrough process parameters. These molten spheres of alumina or similaroxide, typically referred to as primary particles, fuse with one anotherby undergoing collisions at their contact points to form branched, threedimensional chain-like aggregates. The force necessary to breakaggregates is considerable. During cooling and collecting, theaggregates undergo further collision that may result in some mechanicalentanglement to form agglomerates. Agglomerates are thought to beloosely held together by van der Waals forces and can be reversed, i.e.,de-agglomerated, by proper dispersion in a suitable media.

Precipitated abrasives may be manufactured by conventional techniquessuch as by coagulation of the desired particles from an aqueous mediumunder the influence of high salt concentrations, acids or othercoagulants. The particles are filtered, washed, dried and separated fromresidues of other reaction products by conventional techniques known tothose skilled in the art.

A preferred metal oxide will have a surface area, as calculated from themethod of S. Brunauer, P. H. Emmet, and I. Teller, J. Am. ChemicalSociety, Volume 60, Page 309 (1938) and commonly referred to as BET,ranging from about 5 m²/g to about 430 m²/g and preferably from about30m²/g to about 170 m²/g. Due to stringent purity requirements in the ICindustry the preferred metal oxide should be of a high purity. Highpurity means that the total impurity content, from sources such as rawmaterial impurities and trace processing contaminants, is typically lessthan 1% and preferably less than 0.01% (i.e., 100 ppm).

The metal oxide abrasive useful in the dispersion of this invention mayconsist of metal oxide aggregates or individual single sphere particles.The term “particle” as it is used herein refers to both aggregates ofmore than one primary particle and to single particles.

It is preferred that the metal oxide abrasive consists of metal oxideparticles having a size distribution less than about 1.0 micron, a meanparticle diameter less than about 0.4 micron and a force sufficient torepel and overcome the van der Waals forces between abrasive aggregatesthemselves. Such metal oxide abrasives have been found to be effectivein minimizing or avoiding scratching, pit marks, divots and othersurface imperfections during polishing. The particle size distributionin the present invention may be determined utilizing known techniquessuch as transmission electron microscopy (TEM). The mean particlediameter refers to the average equivalent spherical diameter when usingTEM image analysis, i.e., based on the cross-sectional area of theparticle. By force is meant that either the surface potential or thehydration force of the metal oxide particles must be sufficient to repeland overcome the van der Waals attractive forces between the particles.

In another preferred embodiment, the metal oxide abrasive may consist ofdiscrete, individual metal oxide particles having a primary particlediameter less than 0.4 micron (400nm) and a surface area ranging fromabout 10 m²/g to about 250 m²/g.

Preferably, the metal oxide abrasive is incorporated into the aqueousmedium of the polishing slurry as a concentrated aqueous dispersion ofmetal oxides, comprising from about 3% to about 45% solids, andpreferably between 10% and 20% solids. The aqueous dispersion of metaloxides may be produced utilizing conventional techniques, such as slowlyadding the metal oxide abrasive to an appropriate media, for example,deionized water, to form a colloidal dispersion. The dispersion istypically completed by subjecting it to high shear mixing conditionsknown to those skilled in the art. The pH of the slurry may be adjustedaway from the isoelectric point to maximize colloidal stability.

IV. Optional Additives

Other well known polishing slurry additives may be incorporated into thefirst CMP slurry and/or into the second CMP slurry. One class ofoptional additives are inorganic acids and/or salts thereof which may beadded to the first and/or second CMP slurry to further improve orenhance the polishing rate of the barrier layers in the wafer, such astitanium and tantalum. Useful inorganic additives include sulfuric acid,phosphoric acid, phosphonic acid, nitric acid, HF acid, ammoniumfluoride, ammonium salts, potassium salts, sodium salts or othercationic salts of sulfates, phosphates, phosphonates, and fluorides.

V. Methods of Making and Using the First and Second CMP Slurries

The first and second CMP slurries of this invention may be producedusing conventional techniques known to those skilled in the art.Typically, the oxidizing agent and other non-abrasive components, aremixed into an aqueous medium, such as deionized or distilled water, atpredetermined concentrations under low shear conditions until suchcomponents are completely dissolved in the medium. A concentrateddispersion of the metal oxide abrasive, such as fumed alumina, is addedto the medium and diluted to the desired loading level of abrasive inthe final CMP slurry.

The first and second CMP slurries of the present invention may besupplied as one package system including all of the slurry additives.Due to concerns about shipping CMP slurries containing oxidizing agents,and especially hydrogen peroxide, it is preferred that the first andsecond CMP slurries of this invention are prepared and packaged as a CMPprecursor containing every ingredient except the oxidizing agent oragents, shipped to a customer, and combined with hydrogen peroxide orany oxidizing agent at the customer's facility prior to use. Therefore,an aspect of this invention is a first and second CMP composition and/orslurry precursor comprising one or more ingredients selected from thegroup including catalysts, abrasives, and stabilizers in dry or aqueousform but lacking an oxidizing agent. The first and second CMP precursorsare separately combined with at least one oxidizing agent prior to use.

It has been determined that first and second CMP slurries of thisinvention including urea hydrogen peroxide can be formulated by addinghydrogen peroxide to a slurry precursor comprising urea and any otheruseful slurry components to give a urea hydrogen peroxide containing CMPslurries.

A preferred slurry precursor of this invention will comprise a dry oraqueous mixture of urea and at least one metal oxide abrasive.Additional ingredients may be incorporated into the urea containingslurry precursor are useful in first and second CMP slurries.

Although the CMP slurry of this invention may be used to polish any typeof metal layer, the first chemical mechanical polishing slurry of thisinvention has been found to have a high copper, and low tantalum andtantalum nitride polishing rate. In addition, the second chemicalmechanical polishing slurry exhibits desirable low polishing ratestowards the copper layer, while exhibiting a desirable high polishingrate towards the tantalum dielectric insulating layer.

The first and second CMP slurries may be used with any standardpolishing equipment appropriate for use on the desired metal layer ofthe wafer. The first and second CMP slurries of this invention are mostuseful for polishing a substrate including either a tantalum or tantalumnitride portion and a copper alloy containing portion, both over adielectric layer.

When used to polish a substrate including a tantalum or tantalum nitrideportion and a copper portion, the first chemical mechanical polishingslurry is applied to the substrate and the substrate is polished byconventional means using polishing machines and a polishing pad. Whensubstrate polishing using the first CMP slurry is complete, thesubstrate may be washed with deionized water or other solvents to removethe first CMP slurry from the partially polished substrate. Next, thesecond CMP slurry of this invention is applied to the substrate and thesubstrate is polished using conventional techniques in order topreferentially polish the tantalum or tantalum nitride portion incomparison to the copper portion of the partially polished substrate.Once the second polishing step is complete, the second CMP slurry iswashed from the substrate with deionized water or another solvent andthe substrate is ready for further processing.

In both polishing steps, the first and/or the second CMP slurries may beapplied directly to the substrate, to a polishing pad, or to both in acontrolled manner during substrate polishing. It is preferred howeverthat the first and second CMP slurries are applied to the pad whichthereafter is placed against the substrate after which the pad is movedin relationship to the substrate in order to achieve substratepolishing.

The first and second CMP slurries polishes copper, titanium, titaniumnitride, tantalum, and tantalum nitride layers at good rates undercontrollable conditions. The polishing slurries of the present inventionmay be used during the various stages of semiconductor integratedcircuit manufacture to provide effective polishing at desired polishingrates while minimizing surface imperfections and defects.

EXAMPLES

We have discovered a first CMP slurry that polished copper at high rateand tantalum and tantalum nitride layers at lesser rates, and a secondCMP slurry that polishes tantalum and tantalum nitride layers atacceptable rates and copper at comparatively lower rates than the firstCMP slurry.

The following examples illustrate preferred embodiments of thisinvention as well as preferred methods for using CMP slurries of thisinvention.

EXAMPLE 1

In this example, CMP polishing was accomplished using two CMP slurries.The first slurry included an aqueous dispersion of 3.0 weight percent ofa fumed alumina abrasive from SEMI-SPERSE® W-A355 dispersion sold by theMicroelectronics Materials Division of Cabot Corporation, in Aurora,Ill., 2.5 wt% hydrogen peroxide, 3.65 wt% urea, 1.25 wt% tartaric acid,and 50 ppm Triton DF-16 surfactant. The second slurry included all ofthe components of the first slurry plus 0.015 wt% dodecylamine. Bothslurries tested were adjusted to a pH of 7.0 with ammonium hydroxide.

The CMP slurries were tested by two methods. Dissolution rates of Cu andTa in each slurry were tested by electrochemical techniques. The set-upused a rotating disk electrode in a three-electrode cell with a 273potentiostat and Corrosion Software by PAR. Electrochemical data whereobtained with a pre-selected electrode rotation of 500 rpm (or 19.94m/sec maximum) with the rotator and the metal of interest in contactwith the abrasive pad (with a down force of 5.9 psi) or raised above thepad. Thus metal dissolution could be evaluated as its surface wasabraded as well as after abrasion. The former value was assumed to be anapproximate measure of the chemical rate during polishing, while thelater approach gave the corrosion rate of the metal in a given slurry.In typical tests, electrochemical data ware recorded as apotentiodynamic polarization curves, with the potential swept by a rateof 10 mV/sec from about −0.25 V cathodic to the open potential to someanodic potential. The test results are listed in Table 1, columns 3-4.

The copper and tantalum polishing rates, using the same slurries, wereevaluated with an IPEC 472 polishing machine using a down force of 3psi, a table speed of 55 rpm, and a spindle speed of 30 rpm. Theslurries were applied to an IC 1000/SUBA IV pad stack manufactured byRodel at a rate of 200 ml/min. Polishing data are reported in Table 1,columns 5-6.

TABLE 1 Metal Metal Metal dissolution corrosion removal rate rate afterrate in Cu:Ta w/abrasion abrasion polishing Selectivity Slurry Å/minÅ/min Å/min Ratio 1 3% alumina, Cu:240 Cu:36 Cu:2750 2.5% H₂O₂, Ta:140Ta:0.4 Ta:415 6.6:1 3.65% urea, 1.25 wt % tartaric acid, 50 ppm TritonDF-16 2 as 1 plus 0.015% Cu:240 Cu:4.8 Cu:2250 dodecylamine Ta:60Ta:0.12 Ta:50 45:1

Adding a small amount of dodecylamine into the slurry inhibits Taremoval and significantly increases the Cu:Ta selectivity ratio to about45:1. This makes the organic amino compound containing slurry moresuitable for use as copper polishing slurry with a polishing stop on Ta.

The results of the Table 1 also indicate that trends observed inelectrochemical tests are reproduced in polishing: dodecylamine inhibitsTa dissolution with abrasion, and therewith the polishing rate, in amore pronounced fashion than measured on copper. Thus dodecylamine is adissolution inhibitor for Ta.

EXAMPLE 2

This example studies the effect of varying the weight ratio of oxidizingagent and complexing agent is second CMP slurries of this invention oncopper and tantalum dissolution rates. This example used a CMP slurryhaving the following composition; 1.25 weight percent tartaric acid;hydrogen peroxide in an amount identified in Table 2; 3.0 weight percentalumina abrasive (W-A355), 50 ppm Triton DF-16 surfactant with theremainder being deionized water. The pH of the slurries were adjusted to7.0 using ammonium hydroxide.

Polishing results using slurries with different ratios of tartaric acidand hydrogen peroxide oxidizing agent are listed in Table 2. In additionto the compounds listed in Table 2, each slurry contained 3.65wt % urea.The polishing rates were determined using blanket wafers on an IPEC 472polishing tool, with an IC1000/SUBA IV pad stack manufactured by Rodel.The wafers were polished using a 3 psi down force, a table speed of 55rpm, a spindle speed of 30 rpm, and a slurry flow rate of 200 ml/min.

TABLE 2 Cu Ta polishing polishing Run # % tartaric % HPO T:HPO rate,A/min rate A/min 1 1.25 7.5 1:6 2,622 288 2 1.25 5.0 1:4 3,265 304 31.25 2.5 1:2 4,711 274

The polishing results show that increasing the tartaric acid/peroxideweight ratio increases the Cu removal rate without significantlyaffecting the Ta rate.

Metal dissolution and corrosion rates using the same base slurriesdescribed above but with varying tartaric acid amounts (T) and varyinghydrogen peroxide amounts HPO) were evaluated by electrochemical methodsaccording to the method set forth in Example 1 with the results beingreported in Table 3.

TABLE 3 Cu Cu dissolution corrosion rate, Å/min rate Å/min, with afterRun# % tartaric % HPO T:HPO abrasion abrasion 1 0.5 6 1:12 163 16.3 2 16 1:6 163 19.2 3 0.5 2 1:4 240 19.2 4 1 2 1:2 314 38.4 5 3 6 1:2 36057.6 6 1 1 1:1 344 50.4 7 2 2 1:1 336 62.6 8 3 2 1:1 336 62.6

The results from Tables 2 and 3 show that the copper polishing ratecorresponds to the activity measured on copper electrochemically, bothdecreasing with an increase of the weight ratio of oxidizing agent tocomplexing agent, while the tantalum polishing rate and electrochemicaldissolution, are essentially unaffected by the changing composition.

EXAMPLE 3

The trends observed in Example 2, Table 3 were used as the basis forformulating a second chemical mechanical polishing slurry useful forpolishing tantalum and tantalum nitride. The copper and tantalumpolishing rates for several second polishing slurry candidates arereported in Table 4, below. The alumina used in the chemical mechanicalpolishing slurries was a fumed alumina diluted from SEMI-SPERSE® W-A355,an alumina dispersion sold by the Microelectronics Materials Division ofCabot Corporation, in Aurora, Ill.

TABLE 4 Cu PETEOS Cu: Removal Ta Removal Rem. Rate Ta Slurry rate, Å/minrate, Å/min Å/min Sel 1 2% alumina, 5% 651 337 64 1.9:1 H₂O₂, 0.5%tartaric, pH 7.0 2 5% alumina, 5% 260 244 8 H₂O₂, 0.2% tartaric, 0.2%acetic, 2% urea, 0.08% BTA, 50 ppm Triton DF- 16, pH 6 3 3% alumina, 5%66 299 135 1:4.5 H₂O₂, 0.2% acetic acid, 0.08% BTA, 50 ppm Triton DF-16, pH 5.0

Increasing the ratio of oxidizing agent to complexing agent to a valuegreater than 10 significantly decreased copper removal rates as shown inTable 4. Furthermore, the date in Table 4 shows that acetic acid, whichis a poor copper complexing agent, significantly inhibits the copperremoval rate while the tantalum removal rate remains essentiallyunaffected.

What we claim is:
 1. A chemical mechanical polishing slurry comprising:at least one abrasive; at least one oxidizing agent; acetic acid; and atleast one film forming agent, wherein the weight ratio of oxidizingagent to acetic acid is greater than about 10, and wherein the slurryhas a pH of from about 4 to about
 9. 2. The chemical mechanicalpolishing slurry of claim 1 wherein the film forming agent is from about0.01 to about 0.2 wt % benzotriazole.
 3. The chemical mechanicalpolishing slurry of claim 1 wherein the oxidizing agent is hydrogenperoxide.
 4. A chemical mechanical polishing slurry comprising: at leastone abrasive; at least one oxidizing agent; and acetic acid, wherein theweight ratio of oxidizing agent to acetic acid is greater than about 10.5. The chemical mechanical polishing slurry of claim 4 including a filmforming agent.
 6. The chemical mechanical polishing slurry of claim 5wherein the film forming agent is benzotriazole.
 7. The chemicalmechanical polishing slurry of claim 6 including from about 0.01 toabout 0.5 weight percent benzotriazole.
 8. The chemical mechanicalpolishing slurry of claim 4 wherein the acetic acid is present in anamount ranging from about 0.01 to about 3.0 wt %.
 9. The chemicalmechanical polishing slurry of claim 4 having a pH of from about 4 toabout
 9. 10. The chemical mechanical polishing slurry of claim 4 whereinthe abrasive is at least one metal oxide.
 11. The chemical mechanicalpolishing slurry of claim 10 wherein the metal oxide abrasive isselected from the group including alumina, ceria, germania, silica,titania, zirconia, and mixtures thereof.